1. Field of the Invention
The invention relates to a structure of a two-cycle engine and an engine work machine using the structure of the two-cycle engine.
2. Description of Related Art
Various engine work machines, such as mowers, blowers, chain saws, power cutters, and the like, which use a small-sized engine as power source are already well-known.
For example, a mower cuts plants with a blade driven by an engine. To operate at a high efficiency, a high output of the engine is required. Besides, since the mower is often carried by an operator when being used, so a lighter weight is required. Therefore, a two-cycle engine having a smaller size, a lighter weight, and a high output is favored as an engine used in the mower.
In the two-cycle engine, a mixed gas mixing a fuel and air is guided into a combustion chamber formed in a cylinder, and after being compressed through elevation of a piston, the compressed mixed gas is ignited and exploded. Here, when the piston elevates to perform compression in the combustion chamber, a new mixed gas is sucked into a crank case on a lower side of the piston. When the piston descends due to the explosion, the new mixed gas accumulating in the crank case is compressed (single stage compression), and is guided into the combustion chamber again through a scavenging passage. Accordingly, a following operation is repetitively performed in the combustion chamber: a new mixed gas is guided in at the same time when a waste gas after combustion is discharged (scavenging), and the piston elevates again.
To increase an output of the two-cycle engine, it is effective to increase a scavenging efficiency, namely guiding the new mixed gas into the combustion chamber at a high efficiency, and discharging the waste gas at a high efficiency. In order to increase the scavenging efficiency, it is effective to increase a single stage compression ratio to send more mixed gas into the combustion chamber, and a structure with a crank case having a smaller volume is effective to increase the single stage compression ratio.
For example, Patent Literature 1 recites a two-cycle engine structure as follows. The two-cycle engine structure increases the scavenging efficiency by designing an internal structure of the crank case or a structure of the scavenging passage.